Hot-top for ingot mold



United States Patent HOT-TOP FOR INGOT MOLD Application July 10, 1956,Serial No. 596,910 7 Claims. (Cl. 22-147) Pittsburgh, Pa., assignor toColumbus, Ohio, a cor- This invention relates to the casting of metalingot-s and the like in ingot molds having hot-tops for preventing pipeand other imperfections. More particularly this invention relates topermanent hot-tops which are lined with an exothermicallyreactingmaterial capable of producing and retaining sufficient heat to assurehigh yields of sound castings.

Following the completion of refining operations in the process ofmanufacturing steel, the molten steel is teemed into a cast iron moldwhere the steel is allowed to solidify into ingots. As the metal coolsin the mold, imperfections such as pipe are formed in its interior byshrinkage and entrapped gases. For example, when a fully killed steel isteemed into either a big end-up or a big end-down mold, a deepcone-shaped cavity, known as pipe, forms in the upper end of the ingotas a result of shrinkage of the metal during cooling.

The formation of pipe due to metal shrinkage in steel ingots has beenfound to be preventable by the application of a hot-top to the mold forretaining and feeding molten metal to the shrinking ingot. Therefractory material from which such a hot-top is generally constructedor with which it is lined absorbs heat from the metal less rapidly thanthe cast iron walls of the mold so that the top of the ingot remainsmolten until after the remainder of the ingot has solidified. Anoverlying pool of liquid steel is thus furnished which feeds metal downinto the ingot to overcome the shrinkage due to solidification of themetal.

One form of hot-top used in the above manner is made in the form of anouter cast iron shell having a refractory lining in its interior toreduce the heat loss. Only the refractory requires replacement from timeto time while the hot-top casting can be reused many times. Theplacement of cast iron hot-tops on the ingots creates a substantialproblem of hanging ingots, however. When the hot-top casting is placedon the cast iron mold, molten metal tends to run out through the jointor interface formed between them. This runout chills as part of theingot skin to form fins which, in flange-like fashion, hold the ingotsecurely in place in the mold. As a consequence, when the ingot coolsand shrinks within the mold, it is held hanging off of the mold bottom.Tremendous stresses are set up in the ingot skin because of the weightof hanging metal and defects, known in the industry as hanger cracks,are formed in the ingot. Various devices have been employed in the pastto seal the joint between the hot-top and the mold. In most instancesthese devices have been expensive, cumbersome to use, and susceptible todamage by the shrinking metal. For example, a refractory lining orhot-top has been made to extend downwardly into the mold and act as asealing agent for preventing the molten steel being' teemed into themold from reaching the crack between the mold and the hot-top. Inanother attempt to correct this difficulty, the portion of therefractory hot-top extending into the mold was formed with a wiper bladeto prevent molten 2,867,871 Patented Jan. 13, 1959 metal from reachingthe crack between the mold and hottop.

Attempts have been made in the foundry industry to increase theeffectiveness of the hot-top and thereby reduce the amount of metalneeded to feed an ingot. These attempts have generally followed alongthe line of increasing the temperature and heat transfer characteristicsof the hot-top. In this regard, the use of hot-tops lined with anexothermically reacting or heat-producing material has achieved wideacceptance in foundry practice. One such material is shown in U. S.Patent 2,591,105. This patent describes heat producing mixturescontaining aluminum and one or more oxidizing agents along with acontrolled amount of a fluoride. Such mixtures are described as beinguseful in the casting of molten metal, and more particularly, thispatent points out that sand casting risers which are lined with sleevescomposed of this heat-producing material instead of a refractory willprovide much higher casting yields and substantial improvements in thequality of the casting itself.

It is, therefore, one object of the present invention to improve theconstruction of a permanent hot-top and mold for preventing the runoutof metal between the hottop and the mold, while at the same time makingthe most efiicient use of the mold volume without increasing the molddepth to accommodate a projection of the hottop or using wiper strips orother mechanical devices to prevent such runout.

It is another object of the present invention to improve the feedingefiiciency of permanent hot-tops and to reduce the volume of the feederhead required for a particular size of ingot mold.

It is a further object of the present invention to improve theconstruction and simplify the use of permanent hottops having liningsformed of exothermically reacting materials for increasing both theheating and insulating characteristics of the hot-top.

It is still a further object of the present invention to produce animproved ingot by eliminating the laminar layers of metal heretoforeformed when permanent hottops having liners of exothermically reactingmaterials are used on the ingot molds.

Other objects and advantageous features will become apparent as thefollowing description proceeds, taken in connection with theaccompanying drawing in which:

Figure l is a plan view of a hot-top constructed according to presentinvention.

Fig. 2 is a sectional elevation view of a hot-top and ingot mold takensubstantially in plane of line 22 of Fig. 1.

Fig. 3 is a fragmentary sectional elevation view similar to Fig. 2 andshowing a mold and hot-top illustrative of the present invention havingteemed therein a charge of molten metal.

Fig. 4 is a fragmentary sectional elevation view similar to Fig. 3 andshowing the ingot metal at a later time after it has cooled.

While the invention is susceptible of various modifica tions andalternative constructions, a certain preferred embodiment has been shownin the drawing and will be described below in detail. It should beunderstood, however, that there is no intention to limit the inventionto the specific form disclosed but, on the contrary, the intention is tocover all modifications, alternative constructions and equivalentsfalling within the sp rit and scope of the invention as expressed in theappended claims.

Referring more particularly to the drawings, there is shown in Figs. 1-4a cast iron ingot mold 10, of the big end-up type, having a mold cavity11 opening into an upper surface 12. The bottom (not shown) of the moldcan either be integral with the side walls 15 or be formed as a stool onwhich the mold sits. A hot-top, shown 3. generally as 18, is placed onthe top of the mold and comprises a. permanent casting 19 formed with afeeder head cavity 20 extending therethrough and lined with a sleeve orliner 21 made up of 'sand or the like containing an exothermicallyreacting material.

The hot-top casting 19 preferably formed of cast iron, comprises a riserportion 24 terminating in a base 25 approximately the shape of the upperend of the mold 10 on which it is to be used. A pair of lifting hooks 26or the like are formed on the outer surface of the riser 24 forengagement by a hoist or other lifting device. The

riser 24 is formed with a substantially cylindrical shaped cavity 20 andis provided with a pair of opposed recesses 28 adjacent its upper end.

Fitted within the hot-top casting cavity 20 is a complementary sleeve orliner 21 formed of moldable exothermically reacting material and shapedto correspond to the casting cavity 20. The liner 21 is supported withinthe casting by a pair of lugs or projections 29 integrally formedthereon which seat in the recesses 28 on the casting 19. In this manner,the liner can be easily replaced each time the hot-top 18 is used and nomechanical connections or attachments are necessary to support theliner.

One exothermically reacting or heat producing mixture useful inaccordance herewith is sold under the trademark Feedex and has apreferred composition lying within the ranges set forth below:

Percent Aluminum in divided form such as a mixture of powder and sawings30-50 Sodium nitrate or barium nitrate -10 Manganese dioxide or irondioxide or a mixture Reference is made to U. S. Patent No. 2,591,105 fora more detailed description of the above composition. Details as tomethods of forming shapes from the granular material as well asto thevariations in the composition which are dependent on the type of metalbeing cast are set forth in such patent.

An ingot is cast by placing a permanent hot-top casting fitted with alining of exothermically reacting material, as described above, on amold and teeming molten steel into the mold through the hot-top. Pouringis continued until the mold and the hot-top is full (Fig. 3). As themolten steel rises into the hot-top and into contact with the heatproducing lining, the heat of the metal initiates the reaction of theexothermically reacting materials making up the liner. A substantialamount of heat is produced by this reaction and this heat keeps themetal in the hot-top in the molten state. A reservoir or feeder head 31of molten metal is thus kept available for feeding the ingot as itsolidifies and shrinks.

In accordance with the-present invention, provision vis made forpreventing runout of molten metal in the crack 32 between the mold andthe hot-top 18 which results in the formation of hanger cracks in thesolidified ingot. This is accomplished by projecting the bottom surface33 of the hot-top casting 19 inwardly from the mold walls to overhangthe mold cavity 11- opening into the top of the ingot mold 10. Theoverhang is desirably formed by having the bottom opening of the feederhead cavity in the hot-top casting smaller than the correspondingopening of the mold cavity 11.

For most efficiently preventing runout, it has been found that thehot-top casting should extend over the.

mold cavity an equal amount from side wall 15 of the ingot mold and thatthe extent of this overhang should be at least about /2 inch. The moltensteel, when poured intothe mold, contacts this overhanging hot-topsurface 33 and is locally chilled to form a protective skin 35 whichprevents runout in the crack 32 between the hot top casting 19 and mold10. By preventing this runout, hanger fins cannot form and the formationof undesirable hanger cracks is avoided.

In addition to projecting the hot-top casting 19 over the mold cavity 11where it acts as a chill, the contacting surfaces 12, 33 of the mold andthe hot-top are desirably machined smooth and flat. These fiat surfacesafford a tight fit between the mold and hot-top to effectively preventrunout before the molten metal has chilled and a protective skin hasformed.

In order to prevent the chilling action of the hot-top casting fromcausing the ingot metal to freeze over beneath the feeder head beforethe ingot has solidified, the exothermically reacting liner 21 islocated within the hottop casting 19 with its lower surface 36 insubstantially the same plane as the interface or crack 32 between thehot-top casting and the mold. In this manner the heat given off by theliner keeps molten the cast metal near the center of the ingot mold andeffectively localizes the chill effect of the hot-top casting overhang.As a result a metal skin is prevented from forming over the uppersurface of the ingot before the feeding action is complete.

As the molten ingot metal solidifies, the ingot 38 shrinks and pullsaway from the top of the mold as shown in Fig. 4. The peripheralportions of the ingot solidify first and, when molten metal comes incontact with these relatively cooler solid portions, laminar layers ofmetal are formed which cause difliculties when rolling and working theingot. Therefore, provision is made for preventing the flow of moltenmetal 31 from the hot-top over the solidified top portion of the ingot38. To this end the heat producing liner 21 is spaced from the permanenthot-top casting to provide an annular space 39 between them. This spaceis maintained by dimensioning the projections 29 relative to therecesses 28 in the casting 19 such that the minimum clearance isobtained even when the lug contacts the recess wall or any othersuitable spacing means can be provided to maintain the desired spacing.When molten steel is teemed into the ingot mold, it rises into thisannular space 39 between the liner 21 and the casting 19 and is chilledby contact with the metal casting to form an annular collar or dam 40 onthe upper end of the ingot. As the ingot 38 solidifies and shrinks andthe top of the ingot falls below the upper surface of the mold and awayfrom the hot-top, the dam 40 serves to confine the molten metal 31 fromthe hottop to the central area of the mold.

It has been found that the thickness of the annular space 39 between theheat-producing liner 21 and the permanent hot-top casting 19 is animportant factor in producing sound castings and should be at least 5and preferably in the range of M to Vs" for the most desirable results.When this thickness is in the range of A to A", the chill effect of thepermanent casting is sufficient to freeze the annular collar or dam 40and overcome the heatin effects of the heat producing liner 21.Furthermore, as this dam of metal 40 drops out of the annular space 39between the liner 21 and the casting 19 as the ingot 38 shrinks, the airspace remaining serves as an insulation and effectively reduces heatlosses from the linear to the casting.

If the clearance between the liner and the permanent tive and metal inthe annular space will stay molten longer.

In the latter situation the metal penetrates to the top of the sleeveand too high a dam is formed. As a result, a permanent layer of thinmetal sticks to the ingot after the ingot has solidified and rollingmill difliculties are encountered.

In the design of hot-tops for ingot molds according to the presentinvention, it has been found that the volume of the hot-top andheat-producing lining need seldom exceed 8% of the mold capacity toproduce soundingots, and volumes as low as 4% of the mold capacity canbe successfully used with most grades of metal. For most eflicientfeeding, it has been found that the heat-producing lining or sleeveshould have an average inner diameter to height ratio rates of l to l(D:H==1:l) and that the range of ratios for efiicient feeding is from2:1 to 1:2. The thickness of the heat producing lining will depend onthe amount of heat necessary to keep the metal in the feeder head moltenfor the desired length of time.

It has been found also that an exothermically reacting materialsubstantially identical to that employed in making the sleeves butwithout the binder or other materials required in sleeve manufacture,will even further reduce the amount of feeder metal required in ingotmolding. By topping the molten metal with the additional exothennicallyreacting material, loss of heat to the air is reduced to a minimum.Thus, in accordance with the preferred method of employingheat-producing liners of exothermically reacting material in hot-tops, arelatively thin layer of a hot-topping compound containing the sameessential ingredients as the sleeve, i. e. aluminum, an oxidizing agentsuch as iron oxide or manganese oxide, and an alkali fluoride, should beplaced on the molten metal as soon as it has risen to the top of theriser. This hot-topping compound, when placed on the molten metal in thehot-top in a layer of from about one-quarter to three quarters inches indepth and preferably about onehalf inch in depth, adds more heat to themetal in the feeder head, and acts as an effective insulation to preventheat loss from exposed metal in the hot-top.

By improving the construction of hot-tops in accordance with theinvention herein described and claimed, the feeding efiiciency of metalto an ingot is substantially improved inasmuch as the molten metal sofed is confined to the central area of the ingot. This results insubstantial savings in cost over more conventional methods because lessexothermically reacting material, a relatively expensive item, isneeded. Furthermore, the improved construction described herein isextremely successful in preventing runout between the hot-top and themold in a manner heretofore believed to be impractical. The eliminationof runout and its attendant consequence of hanger cracks in the ingothas been accomplished too, in a simple and inexpensive way, and the needfor elaborate devices and pouring methods to prevent such runout isavoided. In addition, substantial savings in cost result from the use ofa permanent hot-top casting in which only the heat-producing lining needbe changed for reuse.

I claim as my invention:

1. In combination, an ingot mold and an improved hot-top, said moldcomprising a metallic body portion having a mold cavity therein openinginto the upper surface thereof, said hot-top comprising a metallic bodyportion having an inner wall defining a cavity extending therethroughand opening into a lower surface of said hot-top, said hot-top cavitybeing lined throughout its length with a liner formed of a moldableexothermically reacting material, said hot-top cavity opening beingsmaller than said mold cavity opening to the extent that when said buttop opening is complementary to said mold opening said hot top surfaceextends at least /2 inch over said mold opening around the entireperiphery thereof, said liner being spaced from the inner wall of saidhot-top to form an annular space between said liner and the wall openingadjacent the lower surface of said hot-top, said space extendingcompletely to the bottom of said hot top and having a thickness in therange of M inch to inch.

2. In a hot-top for use on an ingot mold defining a mold cavity, thecombination of a cast metal member having an inner wall defining acavity therein, said hot-top cavity being smaller than the ingot moldcavity when the hot top is placed on the ingot mold so that said memberoverhangs the mold cavity, with a liner of moldable exothermicallyreacting material arranged within said hot top cavity and spaced fromthe wall thereofto define an annular space extending to the bottom ofthe hot top and opening into the mold cavity, said space being at leastabout inch.

3. In a hot-top for use on an ingot mold defining a mold cavity, thecombination of a cast metal member having an inner wall defining acavity therein, said hot top cavity being smaller than the ingot moldcavity so that said member overhangs the mold cavity when the hot top isplaced on the ingot mold, with a liner of moldable exothermicallyreacting material arranged within said hot top cavity and spaced fromthe wall thereof to define an annular space extending to the bottom ofthe hot top and opening into the mold cavity, said space being in therange of A inch to M; inch, and said liner extending the length of saidhot top cavity.

4. In combination, an ingot mold defining a mold cavity, a cast metalhot-top member having an inner wall defining a cavity therein, saidcavity being smaller than the ingot mold cavity so that said memberoverhangs the mold cavity, and a liner of moldable exothermicallyreacting material arranged within said hot-top cavity and spaced fromthe wall thereof to define an annular space extending to the bottom ofthe hot top and opening into the mold cavity, said space being in therange of 5 inch to 4; inch.

5. In a hot-top for use on an ingot mold having a mold cavity openinginto an upper hot-top supporting surface, the combination comprising, ametallic body having a feeder-head cavity extending therethrough andopening into a lower surface of said body, said feeder-head cavityopening being smaller than the mold cavity opening to the extent thatwhen said feeder-head opening is complementary to the mold opening saidhot-top surface extends at least /2 inch over the mold opening aroundthe entire periphery thereof, and a liner of moldable exothermicallyreacting material arranged within said feederhead cavity and having itslower end adjacent to said lower end adjacent said lower surface, saidliner being spaced from said cavity walls to the extent of 5 inch toinch for defining an annular space extending to the bottom of the hottop and opening adjacent said lower surface.

6. A method of forming a sound ingot comprising teeming molten metalinto an ingot mold having a hot-top on its upper surface defining acavity for containing molten feeder metal, chilling a portion of saidmetal in the vicinity of the joint between said hot-top and said mold toprevent runout and the formation of hanger fins, forming a thin annularmetal dam on said ingot adjacent to said chilled portion and betweensaid chilled portion and the hot top cavity, and adding heat to themetal in the hot-top cavity to keep the metal therein molten for feedingthe center of the ingot as it cools and shrinks, said darn preventingthe molten metal fed to the ingot by the hot-top from solidifying inlayers on top of said chilled portion as the ingot shrinks in the mold.

7. In a metallic ingot mold, the combination with a mold body havingwalls defining a mold cavity and a hot top positioned on said mold bodyand a bottom and an inner wall, said inner wall defining a cavity ofsmaller horizontal cross section than the mold cavity and extendingthrough the-hot top and opening into the mold cavity, said bottomextending over the mold cavity from the mold walls, of a liner ofmoldable exothermically reacting material arranged within said hot topcavity and spaced from thewall thereof to define an annular spaceextending to said horizontal surface and opening into the mold cavity,said space being at least about 5 inch.

(References on following page) References Cited in the file of thispatent' UNITED STATES PATENTS Kenney Dec. 5, 1916 Hitt et a1. July 11,1922 Rowe Sept. 2, 1924 Howard Jan. 13, 1925 Gathmann Dec. 10, 1929 8Haws Mar. 15, 1932 Dumas June 13, 1933 Charman Dec. 11, 1945 Udy Sept.2, 1947 Strauss Apr. 1, 1952 FOREIGN PATENTS France July 13, 1954

